Italian Republic
Who & why: a 2 June 1946 institutional referendum abolishes the monarchy (54% to 46%) just weeks after Umberto II — the "May King" — took the throne from his abdicating father, Victor Emmanuel III. A new Constitution takes effect 1 January 1948. Italy becomes a founding member of NATO in 1949 and the European Coal and Steel Community in 1951, the seed of what becomes the EU.
What it represents: the plain tricolor, with no coat of arms of any kind — the republic breaks with the House of Savoy by removing its shield entirely rather than merely stripping the crown, a cleaner break than several neighboring monarchies-turned-republics managed.
FOTW says the plain tricolour, without arms, has been used since 19 June 1946 and officially since 1 January 1948. Wikipedia's infobox lists the flag as adopted with the founding of the Republic (18 June 1946) and says Article 12 of the Constitution defines it as a vertical tricolour of green, white and red; the civil flag variant is dated 9 November 1948.
- History of the Italian national flag — Flags of the World (CRW Flags) compiled
- Flag of Italy — Wikipedia compiled
Not established: The 1946 decree text was not read. The two sources differ by a day on the 1946 date, and by two years on when it became official.